1. Filed of the Invention
The invention relates to a float for displaying the fill level of a medium in a container, wherein the float, in the intended use, is guided from the wall of the container and is suitable for reflecting electromagnetic waves emitted from a transmitter toward a receiver.
2. Description of Related Art
Floats of the above mentioned type are used, in practice, for fill level measurement based on the radar principle in order to bring about a defined reflection behavior in the area of the surface of the medium whose fill level is to be measured. As is generally known, the reflection factor of electromagnetic waves is dependent on—not only, but also—refraction indices of the media forming the interfaces, and thus, on their permeability and permittivity. The amplitude of the electromagnetic waves reflected without a float is thus dependent on the material characteristics of the media involved, and thus, is dependent on each specific use of a fill level measuring device. In particular, when only the medium interface is used as a reflection surface, the ratio of desired signal intensity to interference signal intensity practically cannot be predicted, which makes it difficult to design a fill level measuring device. These difficulties are alleviated by the use of the above-mentioned float since the reflection of electromagnetic waves is defined by the nature of floats which, in particular, is better than the reflection from media of low permittivity.
Electromagnetic waves emitted from the transmitter, which is normally found above the medium, toward the medium are reflected by the float, which partially extends into the medium, and the reflected waves are received by the receiver, which is also normally found above the medium. Finally, the fill level is calculated using known radar methods. In one of these methods, the fill level is determined from the running time of an electromagnetic pulse. In another method, the frequency of a continual electromagnetic signal is modulated in such a manner that the fill level can be determined using the frequency difference between the emitted and received frequencies (modulated continuous wave).
The float is often located in a reference container, which is normally a long hollow body with relative small cross section surface, wherein the walls of the reference container guide the float. The reference container is normally located inside of the container or next to the container in which the medium is found, whose level is to be determined and the longitudinal axis of the reference container is essentially directed toward the force of gravity. The reference container is connected to the container in such a manner that the fill level of the medium in the reference container coincides with the fill level of the medium in the container (see, FIG. 1).
Due to the small cross section of the surface of the hollow body and due to the mass of the float, interference in the stillness of medium that can occur during filling and removing of the medium are reduced and the measuring accuracy is increased in this manner. On the upper end of the reference container, there is normally a transmitter as well as a receiver for the electromagnetic waves and the reference container is often used as a waveguide for the electromagnetic waves. The floats are often provided with a magnet system and next to the reference container, there is an additional display for the fill level by means of magnetic flap or by means of a display magnet. Displaying the fill level occurs, then, using two independent systems and increases reliability using redundancy, which, however, is presently not an issue.
Floats known from the prior art have a surface on which the electromagnetic waves are reflected. The clearance basically necessary for the float being guided by the walls of the container causes an unforeseeable tilting of the float, through which the reflection characteristics are changed. In this manner, unforeseeable reflections of the electromagnetic waves can occur in the gap created by this tilting between the walls of the container and the float, which detrimentally influences measurement.